The present invention generally relates to a switching method for an electromagnetic switching device. In particular, it may relate to a switching method for a contactor, having at least one load contact which has a current carrying capacity,
wherein the load contact is closed,
wherein the closing of the load contact closes a circuit,
wherein the circuit is opened when a current flowing through the load contact exceeds a current limit value,
and to an electromagnetic switching device which corresponds to it.
Switching methods and switching devices are known. They are used, for example, in a series circuit including a contactor with an upstream or downstream circuit breaker, or in the form of a so-called non-welding contactor. In both cases, the opening of the circuit provides short-circuit protection for the contactor.
In some applications, an extremely high surge current flows briefly when the circuit is closed. In the case of transformers, the surge current may amount to 20 to 30 times the continuous current, and in the case of capacitors it may even amount to 50 to 100 times the continuous current. The switching device must always be designed such that it can safely switch even this high surge current. The switching device therefore has to be considerably over-designed in order to switch transformers or capacitors, in comparison to the continuous current to be carried.
An object of an embodiment of the present invention is to specify a switching method for an electromagnetic switching device and for the electromagnetic switching device corresponding thereto. The switching device may be designed to be smaller, without changing the continuous current which can be carried.
An object may be achieved by the circuit being closed again automatically when the current flowing through the load contact falls below the current limit value again as a result of the opening of the circuit. Further, the current limit value may be, at most, as great as the current carrying capacity.
This is because, when the load is connected to the power supply system, the circuit is initially closed, and is then opened again before the current carrying capacity of the load contact is exceeded. The load contact is admittedly closed again immediately after this. The current surge which occurs when the load contact is closed for the second time is, however, considerably less than the current surge which occurred previously. As a rule, this second current surge no longer exceeds the current carrying capacity of the load contact. This thus means, for example when connecting a capacitor, that it is possible to use a switching device in which the current carrying capacity is, for example, 25 times the continuous current to be carried instead ofxe2x80x94as in the prior artxe2x80x9475 to 100-times the continuous current to be carried.
When the load contact is opened in order to open the circuit when the current limit value has been exceeded, no dedicated switch is required to open the circuit.
When the current flows through an electromagnetic drive, which is connected in series with the load contact, with the circuit closed, which electromagnetic drive opens a switching element, which is connected in series with the electromagnetic drive, when the current limit value is exceeded, the circuit can be opened in a particularly simple manner when the current limit value is exceeded. If a pair of contact elements are electrically conductively connected by a contact link to which a pressure spring applies a pressure force in the direction of the pair of contact elements, in order to close the load contact, and the electromagnetic drive acts directly on the contact link when the current limit value is exceeded and lifts it off the pair of contact elements, the load current monitoring element responds particularly quickly.
If a deflection lever which is associated with the electromagnetic drive is deflected from a rest position by a plunger, which is associated with the electromagnetic drive, when the current limit value is exceeded, and the deflection of the deflection lever lifts the contact link off the pair of contact elements, this results in the electromagnetic switching device being particularly simple and compact.